MdeModulePkg:DxeHttpLib: Add checks in HttpGenRequestMessage API

MdeModulePkg:DxeHttpLib: Add checks in HttpGenRequestMessage API

HttpGenRequestMessage assumes that HTTP message would always
contain a request-line, headers and an optional message body.
However, subsequent to a HTTP PUT/POST request, HTTP requests
would contain just the message body. This patch supports
creation of such request messages with additional checks.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Hegde, Nagaraj P <nagaraj-p.hegde@hpe.com>
Reviewed-By: Wu Jiaxin <jiaxin.wu@intel.com>
Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>